Coolant in oil. Need help identifying cause.

The intake bolts like the head bolts penetrate into the cooling jackets. The powder that came out with the intake bolts was either corrosion from coolant leakage or the failed remainder of some sort of sealer. The intake and cylinder head fastener holes are open to the cooling passages or in the intake case some open into oily places so must use a sealer on the threads that is proof against failure by coolant which carry's either some sort of glycol ethylene or propylene being the most common which is a solvent material and contains an Inorganic Acid Technology or the an Organic Acid Technology (OAT) like original Dexcool or Hybred Organic Acid Technology that the Euros and Asians like but these are not the same mix where Euro HOAT uses a silicate base which is good where people introduce hard water into the cooling system while the Asian’s use a phosphate inhibitor that is intolerant of the chemistry of hard water so this coolant must be blended with distilled or deionized water. Which really should be used in all coolant solutions, not the stuff from your house’s or a gas station’s water tap. All of these chemistries have differing reactions and consumable additive life times. So it’s easy to find corrosion or deposition products with fasteners which often are plated thus developing other reaction in their joints. Note for Chevrolet and others that you don’t find plated fasteners on or in the engine because the plating provides another reactant in the joint.

Teflon tape is really meant to seal plumbing threads which in the US are a tapered thread where bolted joints are a straight thread. To a large extent straight threads seal better with paste sealer than tape, though Chevy puts a Teflon coating on their head bolts but is usually damaged by the time you get them. In the past and to some extent I still use Teflon based or infused plumbers thread sealer. But I find it’s not always resistant to constant exposure to engine coolant or oil and is certainly unsuitable for solvent fuels like gasoline. I’ve pretty much returned to old fashion Permatex No 2 or 3 as it doesn’t depend on a cure to form a washout resistant thread seal and it’s lubricity is close to 30 wt engine oil which is used as the thread lubrication material for most stated fastener torque tables You may assume this is true unless otherwise stated. This establishes the ratio of torque applied to stretch achieved when tightening a fastener. So changes in the lubricity within the threads from bare to moly or Teflon or RTV in the joint changes the torque applied to stretch achieved ratio.

So you need a sealer and lubricant in the bolted joints that is resistant to coolant and oil while sealing straight threads and providing thread lubricity that acts like 30 wt engine oil all at the same time.

Bogie